1. Field of the Invention
The present invention relates to an input image signal processing method particularly useful for the case where the reproduction range of an output device is not sufficient for obtaining a complete reproduction of the image characteristics of an input image signal.
2. Related Background Art
The gradation range of a television signal, for example, is in general considerably wide. Conventionally, a gradation correction has been performed to obtain a hard copy with a printer when the gradation reproducing range of the printer is narrower than the gradation range of a television signal. In one example of the related art gradation correction methods, a histogram is formed in which an input image signal is represented by classifying it in accordance with its gradation level. Based upon the histogram, the maximum gradation level of the input image signal is made to coincide with that of a printer, and the minimum gradation level of the input image signal is made to coincide with that of the printer. With this method, it has been possible to always obtain a high contrast image. However, it involves some problems that even a flat image which inherently has no contrast is reproduced with contrast and an image of dark gradation is reproduced as a completely dark portion.
In the case where an input signal is a color image signal, to make the saturation range of an input color image signal agree with the saturation reproducing range of an output device such as a printer, the portion of an input color image signal exceeding the saturation reproducing range has been heretofore compressed to the maximum value of the reproducing range. As a result, saturation continuity of the input color image is destroyed, resulting in a deformed output image.